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Appl. Environ. Microbiol. doi:10.1128/AEM.01518-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Transcriptional regulation of the pdt gene cluster of Pseudomonas stutzeri KC involves an AraC/XylS family transcriptional activator (PdtC) and the cognate siderophore pyridine-2,6-bis(thiocarboxylic acid) (PDTC)

Department of Microbiology and Molecular Genetics, University of Vermont, Burlington VT 05405, USA

^* To whom correspondence should be addressed. Email: talewis{at}zoo.uvm.edu.

	Abstract

In order to gain an understanding of the molecular mechanisms dictating production of the siderophore and dechlorination agent pyridine-2,6-bis(thiocarboxylic acid) (PDTC) we have begun characterization of a gene found in the pdt gene cluster of Pseudomonas stutzeri KC predicted as having a regulatory role. That gene product is an AraC-family transcriptional activator, PdtC. Quantitative RT-PCR and expression of transcriptional reporter fusions were used to assess a role for pdtC in transcription of pdt genes. PdtC and an upstream, promoter-proximal DNA segment were required for wild type levels of expression from the promoter of a predicted biosynthesis operon (P_pdtF). At least two other transcriptional units within the pdt cluster were also dependent upon pdtC for expression at wild type levels. The use of a heterologous, P. putida host demonstrated that pdtC and exogenously added siderophore were necessary and sufficient for expression from the pdtF promoter, i.e. none of the PDTC utilization genes encoded within the pdt cluster were required for transcriptional signaling. Tests using the promoter of the pdtC gene in transcriptional reporter fusions indicated siderophore-dependant negative autoregulation similar to that seen with other AraC-type regulators of siderophore biosynthesis and utilization genes. The data increase the repertoire of siderophore systems known to be regulated by this type of transcriptional activator, and have implications for PDTC signaling.